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Medical Author:

Dennis Lee, MD

Dennis Lee, MD

Dr. Lee was born in Shanghai, China, and received his college and medical training in the United States. He is fluent in English and three Chinese dialects. He graduated with chemistry departmental honors from Harvey Mudd College. He was appointed president of AOA society at UCLA School of Medicine. He underwent internal medicine residency and gastroenterology fellowship training at Cedars Sinai Medical Center.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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In this Article

• What is colonoscopy?
• What is virtual colonoscopy?
• Comparing virtual colonoscopy and optical colonoscopy
• My personal approach to recommending virtual versus optical colonoscopies
• Virtual Colonoscopy Index

What is virtual colonoscopy?

Virtual colonoscopy is a technique that uses a computerized tomographic (CT) scan (a type of three-dimensional x-ray) to construct virtual images of the colon that are similar to the views of the colon obtained by direct observation by optical colonoscopy.

In preparation for virtual colonoscopy, the day before the examination the colon is emptied using laxatives in a manner similar to optical colonoscopy. During the examination, a small tube is inserted into the anus to inject and fill the colon with air. Unlike with optical colonoscopy, this tube is not advanced into the colon. The CT scan then is performed, and the scans are manipulated by computer software to form virtual images of the colon. When properly performed, virtual colonoscopy can be as effective as optical colonoscopy. It can even find polyps "hiding" behind folds that occasionally are missed by optical colonoscopy. The scanning takes only 10 minutes, and usually no conscious sedation is necessary.

In October, 2007, researchers from University of Wisconsin published in the New England Journal of Medicine a study comparing traditional optical colonoscopy to virtual colonoscopy. More than six thousand patients over age 50 were evenly divided to undergo either optical or virtual colonoscopy. The researchers found that virtual colonoscopy was as effective as optical colonoscopy in detecting polyps larger than 5mm.

Comparing virtual colonoscopy and optical colonoscopy

• Virtual colonoscopy is less invasive and faster to perform than optical colonoscopy and does not require conscious sedation.
  
  
• Even though virtual colonoscopy is less invasive than optical colonoscopy, virtual colonoscopy still involves injecting air into the colon, which can be uncomfortable for some patients. On the other hand, with adequate conscious sedation, patients usually experience little or no discomfort with optical colonoscopy.
  
  
• Virtual colonoscopy is not as reliable as optical colonoscopy in detecting small polyps (less than 5mm in size). Even though most experts believe that polyps smaller than 5mm are usually benign, some small polyps can be cancerous or become cancerous if not removed.
  
  
• Virtual colonoscopy is not as accurate as colonoscopy in finding flat cancers or polyps that are not protruding, that is, are not polyp-like.
  
  
• Virtual colonoscopy cannot remove polyps. If polyps are found by virtual colonoscopy, then optical colonoscopy must be performed to remove the polyps. Therefore, many individuals having virtual colonoscopy will have to undergo a second procedure, optical colonoscopy.
  
  
• Even though the amount of radiation exposure with virtual colonoscopy is considered safe, the long term radiation effects of mass screening with CT is not known.